In recent years, such technologies as connecting a portable device such as a smart phone and a tablet with a digital television set via a network, operating the digital television set through the portable device, and receiving information from the digital television are started to be used.
Furthermore, there have been demands for publishing a certificate showing that a specific broadcast program has been viewed to a user who has viewed the program on digital television, and execution of various processes between other devices and the portable device on the basis of such a certificate. If a certificate is altered or acquired in an unauthorized manner, however, unauthorized manipulation through a portable device may be made possible.